Spare time (even in occasional dollops) might be channelled towards helping the Boston Public Library transcribe their recently digitised Anti-Slavery manuscripts!

(Or if squinting to decipher handwriting isn't quite your forte, one of these many quite other projects on the Zooniverse collection: classifying scientific illustrations in Victorian-era periodicals; tracing outlines of strewn objects in photographs to teach algorithms to recognise beach litter; counting seals in timelapse video footage recorded in Antartica... I rather fancy the manatee acoustics one, myself.)